Before we introduce you to the Onyx mixers’ Perkins EQ
section, we should probably introduce you to its designer, Cal Perkins.
Along with Greg Mackie, Cal has been the driving force behind Mackie innovations
like XDR mic preamps, HR Series monitors and more not to mention his
30-plus years of experience designing classic audio gear for other folks.

To create his all-new Perkins EQ, Cal started with the Wien Bridge circuit
topology - a very musical design inspired by the hallowed "British" desks
of the 60s and 70s. This design essentially trades boost/cut capability
for a wider, highly musical Q filter. But Cal, being the cool dude he
is, decided that you deserve a better bargain.

To get past the tradeoffs of the Wien Bridge, he wrote a mind-numbing
20 pages of equations describing this seemingly simple circuit in complete
detail. After solving the equations with overclocked brainpower, Cal was
able to specify capacitor and resistor values that would give Onyx mixers
an extra 6dB of control (±15 dB) without excessively narrowing the "Q"
or bandwidth of the filters.

What this all means, when the fingers hit the knobs, is that you have
four bands of utterly primo sounding EQ at your command to massage the
most messed-up of singers and musicians. And oh, what a musical four bands
the Onyx 80 Series give you!

Mono Channels feature:

High: ±15 dB @ 12 kHz

High Mid: ±15 dB, sweepable from 400 Hz to 8 kHz

Low Mid: ±15 dB, sweepable from 100 Hz to 2 kHz

Low: ±15 dB @ 80 Hz

While Stereo Channels feature:

High: ±15 dB @ 12 kHz

Mid: ±15 dB @ 2.5 kHz

Low: ±15 dB @ 80 Hz

Next, Cal employed combining filters for minimum phase shift, making the
entire EQ section as musical as possible. Finally, he added an individual
hardware bypass on every channel that completely removes the EQ circuitry
from the signal path. On the seventh day, he rested. The end result is a
sweet, very musical analog EQ section that sounds great when it's "in" and
is completely invisible when it's "out".

* The truth is that there were almost as many different types of "British
EQ" circuitry as there were British mixing console designers in the 1960’s
and 1970’s. But the Wein Bridge topology Cal used for Perkins EQ is generally
considered to be among the sweetest. (You can now pick the "Debunking Audio
Myths" category on Audio Jeopardy.)